The Diabetes Prevention Trial of Type 1 Diabetes (DPT-1) is a nationwide study designed to determine whether it is possible to prevent or delay the onset of insulin-dependent diabetes mellitus, (Type 1 or IDDM). First degree relatives of people with IDDM have been screened for islet cell antibodies (ICA) (RPN # 94-01-25-06). The aim of this study is to define the risk category for developing diabetes mellitus for those non-diabetic relatives age 3 to 45 years who have screened positive for ICA and consent to undergo further evaluation. Those individuals who screened positive will be invited to undergo "staging" which consists of confirmation of ICA status., measurement of insulin autoantibodies (IAA), determination of HLA status, an intravenous glucose tolerance test (IVGTT) on two separate occasions, and an oral glucose tolerance test.